In a conventional three-way or three-ported flow-regulating valve an inflow channel is connected to an outflow channel via a throttle valve, a pressure-relief valve being connected in parallel thereto. The quantity of liquid moving through the outflow channel is determined by the pressure drop across the throttle valve, this drop being a function of the shutter opening in the throttle valve and of the pressure in the inflow channel. The force exerted by a biasing spring in the pressure-relief valve establishes an upper limit for the pressure drop across the throttle valve, the pressure-relief valve opening whenever the pressure difference between the inflow channel and the outflow channel exceeds this upper limit.
A disadvantage of conventional three-way flow-regulating valves is that a jump in the pressure of the fluid in the inflow channel, occasioned for example by the activation of an auxiliary pump, results in a sudden increase in the flow rate through the outflow channel. Such sudden flow-rate increases may have a deleterious effect on production and upon the life of hydraulic machinery.